Xie Hai-Yang, He You-Zhao, Gan Wu-Er, Fu Guo-Ni, Li Lian, Han Fang, Gao Yong
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, China.
J Chromatogr A. 2009 Apr 10;1216(15):3353-9. doi: 10.1016/j.chroma.2009.01.070. Epub 2009 Jan 29.
A simple and efficient dual preconcentration method of on-column liquid-liquid-liquid microextraction (LLLME) coupled with base stacking was developed for capillary zone electrophoresis (CZE) in this paper. Four N-methyl carbamates were used as target compounds to evaluate the enrichment means. The carbamates in sample solutions (donor phase) were extracted into a dodecanol phase immobilized on a porous hollow fiber, hydrolyzed and back extracted into 0.20 microL running buffer (acceptor phase) of 30 mmol/L methylamine hydrochloride (pH 11.6) containing 0.5 mmol/L tetradecyltrimethylammonium bromide inside the hollow fiber, stacked further with 0.5 mol/L NaOH injected at -10 kV for 60s, and separated by CZE. Analytical parameters affecting the LLLME, base stacking and CZE were investigated, including sample solution volume, pH and temperature, extraction time, stirring rate, buffer component, buffer pH, NaOH concentration, stacking time, etc. The enrichment factors of the carbamates were higher than 1100. The relative standard deviation (RSD) of peak height and limits of detection (LODs) were 4.5-5.5% (n=6) and 2-4 ng/mL (S/N=3) for standard solutions, respectively. The proposed method was applied to the analysis of vegetable and fruit samples with the RSD less than 6.0% (n=3) and LODs of 6-10 ng/g (S/N=3). The calibration solutions were prepared by diluting the stock solutions with blank sample solutions, and the calibration concentrations ranged from 0.012 to 1.0 microg/mL (r>0.9951). The analytical results demonstrated that the LLLME coupled with base stacking was a simple, convenient and reliable on-column sample pretreatment method for the analysis of anionic analytes in CZE.
本文开发了一种简单高效的柱上液-液-液微萃取（LLLME）与碱堆积相结合的双重预富集方法，用于毛细管区带电泳（CZE）分析。使用四种N-甲基氨基甲酸酯作为目标化合物来评估富集方法。样品溶液（供体相）中的氨基甲酸酯被萃取到固定在多孔中空纤维上的十二烷醇相中，水解后再反萃取到中空纤维内部含有0.5 mmol/L十四烷基三甲基溴化铵的30 mmol/L盐酸甲胺（pH 11.6）的0.20 μL运行缓冲液（受体相）中，通过在-10 kV下注入0.5 mol/L NaOH 60 s进一步堆积，然后通过CZE分离。研究了影响LLLME、碱堆积和CZE的分析参数，包括样品溶液体积、pH和温度、萃取时间、搅拌速率、缓冲液成分、缓冲液pH、NaOH浓度、堆积时间等。氨基甲酸酯的富集因子高于1100。标准溶液的峰高相对标准偏差（RSD）和检测限（LOD）分别为4.5-5.5%（n=6）和2-4 ng/mL（S/N=3）。该方法应用于蔬菜和水果样品的分析，RSD小于6.0%（n=3），LOD为6-10 ng/g（S/N=3）。校准溶液通过用空白样品溶液稀释储备溶液制备，校准浓度范围为0.012至1.0 μg/mL（r>0.9951）。分析结果表明，LLLME与碱堆积相结合是一种用于CZE中阴离子分析物分析的简单、方便且可靠的柱上样品预处理方法。
